Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
International Research Center for Neurointelligence (WPI-IRCN), UTIAS, The University of Tokyo, Tokyo, Japan.
Nature. 2021 Dec;600(7890):686-689. doi: 10.1038/s41586-021-04125-7. Epub 2021 Nov 24.
Synaptic transmission involves cell-to-cell communication at the synaptic junction between two neurons, and chemical and electrical forms of this process have been extensively studied. In the brain, excitatory glutamatergic synapses are often made on dendritic spines that enlarge during learning. As dendritic spines and the presynaptic terminals are tightly connected with the synaptic cleft, the enlargement may have mechanical effects on presynaptic functions. Here we show that fine and transient pushing of the presynaptic boutons with a glass pipette markedly promotes both the evoked release of glutamate and the assembly of SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins-as measured by Förster resonance transfer (FRET) and fluorescence lifetime imaging-in rat slice culture preparations. Both of these effects persisted for more than 20 minutes. The increased presynaptic FRET was independent of cytosolic calcium (Ca), but dependent on the assembly of SNARE proteins and actin polymerization in the boutons. Notably, a low hypertonic solution of sucrose (20 mM) had facilitatory effects on both the FRET and the evoked release without inducing spontaneous release, in striking contrast with a high hypertonic sucrose solution (300 mM), which induced exocytosis by itself. Finally, spine enlargement induced by two-photon glutamate uncaging enhanced the evoked release and the FRET only when the spines pushed the boutons by their elongation. Thus, we have identified a mechanosensory and transduction mechanism in the presynaptic boutons, in which the evoked release of glutamate is enhanced for more than 20 min.
突触传递涉及两个神经元之间突触连接处的细胞间通讯，并且已经广泛研究了该过程的化学和电形式。在大脑中，兴奋性谷氨酸能突触通常形成在学习过程中扩大的树突棘上。由于树突棘和突触前末端与突触小间隙紧密相连，因此扩大可能对突触前功能具有机械作用。在这里，我们表明，用玻璃吸管对突触前末梢进行精细和短暂的推动，可明显促进谷氨酸的诱发释放以及 SNARE（可溶性 N-乙基马来酰亚胺敏感因子附着蛋白受体）蛋白的组装-通过 Förster 共振转移（FRET）和荧光寿命成像在大鼠切片培养物中进行测量。这两种效应均持续超过 20 分钟。增加的突触前 FRET 独立于细胞质钙（Ca），但依赖于 SNARE 蛋白的组装和末梢中的肌动蛋白聚合。值得注意的是，低渗蔗糖（20 mM）溶液对 FRET 和诱发释放均具有促进作用，而不会引起自发释放，这与高渗蔗糖溶液（300 mM）形成鲜明对比，后者本身会引起胞吐作用。最后，双光子谷氨酸光解诱导的脊柱扩大仅在脊柱通过其伸长推动末梢时，才会增强诱发释放和 FRET。因此，我们已经确定了突触前末梢中的机械感觉和转导机制，其中谷氨酸的诱发释放增强超过 20 分钟。
